A court in Girona has sentenced Lianne Smith to 30 years in prison for the murder in 2010 of her two small children in the Costa Brava resort of Lloret de Mar. The jury found that although she was "gravely disturbed" at the time, she was aware of what she was doing and acted out of free will.

The jury accepted the defence argument that Smith, 45, had suffered a bout of "pathological depression" on learning that her partner and the children's father, Martin Smith, had been arrested on charges of paedophilia. The couple had earlier agreed to a suicide pact should they ever be separated. They fled to Barcelona in 2007 after Martin Smith was put on the Metropolitan police's most wanted list. He was jailed in 2010 on charges of abusing Lianne Smith's eldest daughter over a period of 10 years and was found hanged in his cell at Strangeways prison in Manchester in January this year.

A psychiatrist from the Institute of Forensic Medicine in Girona told the court Lianne Smith "knew she had committed a crime, but for her the worst that could happen would be for her children to be taken into care", something she believed would happen once Martin Smith had been arrested. Judge Garcia Morales said he was imposing the minimum sentence for murder because he considered that, although responsible for her actions, Smith was suffering from a degree of "mental disturbance" when she committed the crimes.

The jury concluded that there was sufficient evidence to suggest that Smith's faculties were neither "completely nor gravely" disturbed when she decided to murder her children, Daniel, 11 months, and Rebecca, five, by asphyxiating them with a plastic bag in their hotel bedroom, given that she was able to make a coherent statement to police and had left several notes in the room.

Smith presented herself at the reception in the Hotel Miramar in Lloret de Mar at about 1.30pm on 18 May 2010 and said she had killed her children. She had spent the night with the two corpses in the bedroom and had apparently attempted suicide. In one of the notes she wrote that Martin Smith was innocent and the family had been destroyed by her elder daughter, who had accused him of paedophilia.

The prosecutor, Victor Pillado Quintas, said in his opening statement: "Taking advantage of the trust the children would have had in their mother, she took her son in her arms and put a bag over his head, closing it around his neck. She did not stop tightening the bag until she had killed him. Immediately, she did the same to the five-year-old, closing the same bag around her neck and tightening it until she killed her daughter." The jury was shown a video of a statement Smith made to police the day after the children died, filmed in a room next to where the killings took place. She said: "I gave my children a three-day holiday, a perfect holiday, we were very, very happy. We came here with nothing, we had left everything again. This was the end of the road, I knew my children would be taken back to England. My daughter didn't want to go, she didn't want to leave me.

"I know it's not right to take another life, but I felt I was in a corner and my intention was for me and my children to go. It was not just the children, it was me as well."

The two children were buried in a niche in the municipal cemetery in Lloret de Mar. No family members attended the funeral.

• This article was amended on 4 July 2012. The original said Martin Smith was convicted on charges of abusing his eldest daughter. He was jailed for abusing Lianne Smith's daughter by a previous relationship. She has waived her right to anonymity.